This invention relates to control of an infinite speed ratio continuously variable transmission for vehicles.
Tokkai Hei10-267116 published by the Japanese Patent Office in 1998 discloses an infinite speed ratio continuously variable transmission for a vehicle (referred to hereafter as IVT) which can vary a speed ratio continuously to infinity by combining a reduction gear and a planetary gear set with a toroidal continuously variable transmission (referred to hereafter as CVT).
The rotation of an engine is input to the CVT whereof the speed ratio can be varied continuously, and a reduction gear having a fixed speed change ratio. The rotation of an output shaft of the CVT is input to a sun gear of the planetary gear set, and the rotation of an output shaft of the reduction gear is input to a planet carrier of the planetary gear set. The final output shaft of the IVT is joined to a ring gear of the planetary gear set. The output shaft of the reduction gear and planet carrier are joined via a power recirculation clutch. The output shaft of the CVT is also joined to the final output shaft via a direct clutch.
In a power recirculation mode wherein the power recirculation clutch is engaged and the direct clutch is disengaged, the direction and speed of output rotation of the final output shaft varies according to the difference of the speed ratio of the CVT, and the speed ratio of the reduction gear. Specifically, the speed ratio Ii of the IVT, i.e., the value of the input shaft rotation speed/final output shaft rotation speed of the IVT varies from a negative value to a positive value. Also, at the point where the rotation direction of the final output shaft varies, the speed ratio of the IVT Ii is infinite, and the final output shaft is stationary. This point is referred to as a geared neutral point (GNP).
On the other hand, in a direct mode wherein the power recirculation clutch is disengaged and the direct clutch is engaged, the rotation of the CVT output shaft is output to the final output shaft without modification, so the speed ratio Ii of the IVT is equal to the CVT speed ratio IC.
The change-over between the power recirculation mode and the direct mode is performed at a rotation synchronous point (RSP) at which the IVT speed ratio Ii of each mode coincide with each other. If we define the inverse of the IVT speed ratio Ii as an IVT speed ratio factor "Egr", the IVT speed ratio factor "Egr" increases as the vehicle starts to move forward and accelerate in the power recirculation mode. The CVT speed ratio Ic also increases at that time. At the RSP, a mode change-over is performed, and in the subsequent direct mode, the IVT speed ratio factor "Egr" continues to increase but the CVT speed ratio IC decreases. Also, reversing of the vehicle is performed only in the power recirculation mode, wherein the IVT speed ratio factor "Egr" increases in negative value and the CVT speed ratio Ic approaches O together with the acceleration of the vehicle.
During a kickdown operation of the IVT, i.e., an increases of the speed ratio of the IVT due to the depression of an accelerator pedal of the vehicle by a driver, or during a shift-up operation of the IVT when the driver releases his foot from the accelerator pedal, a rapid speed change is required. If this speed change is performed beyond the rotation synchronous point RSP, the CVT speed ratio Ic is temporarily fixed at the rotation synchronous point RSP, and the engagement and disengagement of the power recirculation clutch and direct clutch are changed over. However, this change-over delays variation of the IVT speed ratio Ii.
One way of enabling rapid speed change would be to make the change-over between the power recirculation mode and direct mode while the clutches are partially engaged. However, the change-over of the operation mode of the IVT in the course of IVT speed ratio control towards a target value may cause the IVT speed ratio to overrun the target value. In this case, the shift direction of the IVT abruptly reverses immediately after the change-over of operation mode so as to cancel out the overrun, and the driver may experience an uncomfortable feeling due to the abrupt change of the shift direction of the IVT.
It is therefore an object of this invention to perform the change-over between the power recirculation mode and the direct mode of the IVT smoothly in a short time.
In order to achieve the above object, this invention provides a speed change controller for such an infinite speed ratio continuously variable transmission for use with a vehicle that comprises an input shaft, a continuously variable transmission which transmits a rotation speed of the input shaft to a continuously variable transmission output shaft at an arbitrary speed ratio, a fixed speed ratio transmission which transmits the rotation speed of the input shaft to a fixed speed ratio transmission output shaft at a fixed speed ratio, a planetary gear set comprising a first rotation member joined to the continuously variable transmission output shaft, a second rotation member joined to the fixed speed ratio transmission output shaft, and a third rotation member which varies a rotation direction and a rotation speed according to a difference between a rotation speed of the first rotation member and a rotation speed of the second rotation member, a direct clutch which connects and disconnects the continuously variable transmission output shaft and the third rotation member, and a power recirculation clutch which connects and disconnects the fixed speed ratio transmission output shaft and the second rotation member.
The speed change controller comprises a sensor which detects a running state of the vehicle, a sensor which detects a real speed ratio of the infinite speed ratio continuously variable transmission, and a microprocessor programmed to set a target speed ratio of the infinite speed ratio continuously variable transmission based on the running state, determine whether or not the target speed ratio has varied beyond a predetermined speed ratio, determine a priority of controlling the power recirculation clutch and direct clutch, and controlling the speed ratio of the continuously variable transmission, so that, when the target speed ratio has varied beyond the predetermined speed ratio, the real speed ratio of the infinite speed ratio continuously variable transmission varies in the same direction until it reaches the target speed ratio, and control the power recirculation clutch and direct clutch, and control the speed ratio of the continuously variable transmission, according to the priority.
This invention also provides a speed change controller comprising a mechanism for detecting a running state of the vehicle, a mechanism for detecting a real speed ratio of the infinite speed ratio continuously variable transmission, a mechanism for setting a target speed ratio of the infinite speed ratio continuously variable transmission based on the running state, a mechanism for determining whether or not the target speed ratio has varied beyond a predetermined speed ratio, a mechanism for determining a priority of controlling the power recirculation clutch and direct clutch, and controlling the speed ratio of the continuously variable transmission, so that, when the target speed ratio has varied beyond the predetermined speed ratio, the real speed ratio of the infinite speed ratio continuously variable transmission varies in the same direction until the real speed ratio reaches the target speed ratio, and a mechanism for performing control of the power recirculation clutch and direct clutch, and of the speed ratio of the continuously variable transmission, according to the priority.
This invention also provides a speed change control method for the infinite speed ratio continuously variable transmission for use with a vehicle. The method comprises detecting a running state of the vehicle, detecting a real speed ratio of the infinite speed ratio continuously variable transmission, setting a target speed ratio of the infinite speed ratio continuously variable transmission based on the running state, determining whether or not the target speed ratio has varied beyond a predetermined speed ratio, determining a priority of controlling the power recirculation clutch and direct clutch, and controlling the speed ratio of the continuously variable transmission, so that, when the target speed ratio has varied beyond the predetermined speed ratio, the real speed ratio of the infinite speed ratio continuously variable transmission varies in the same direction until the real speed ratio reaches the target speed ratio, and performing control of the power recirculation clutch and direct clutch, and of the speed ratio of the continuously variable transmission, according to the priority.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.